Gas lift valves are used primarily in oil well production for injecting gas into the fluid to be produced lifting the fluid to the surface without pumping.
The well generally has a well tubing with a casing surrounding the well tubing. Side pockets are formed on the tubing with passages communicating with the well casing. Gas lift valves are positioned in the side pockets to control flow through the passage formed between the casing and tubing such that when the casing is pressurized, pressure will be released into the tubing at a predetermined rate to aerate the fluid therein to raise it to the surface.
Heretofore, the general practice has been to employ a bellows diaphragm in the valve which is internally biased to allow pressure to act against the sides of the diaphragm to open the valve or to use an externally biased diaphragm such that the well casing pressure expands the diaphragm and opens the valve. When utilizing high pressures in the range of 2,000 psi the pressure often causes premature failure of the bellows. A rupture of the bellows requires that the valve be repaired or replaced and considerable production is lost for significant length of time. In addition, a direct actuation of the bellows causes significant variations in the opening and closing of the valve because of the varying pressure in the well. Vertical vibrations cause horizontal movement of the valve ball relative to the seat causing excessive wear on valve ball and seat. Vertical vibrations of the valve stem also cause additional lateral vibrations of the stem, causing excessive valve chatter and premature failure of the valve.